Microbial growth on outdoor-weathered plastics

Microbial growth, presumably fungus or mildew, has been found growing on samples of aromatic engineering thermoplastics after 6–24 months of outdoor exposure at Miami, Florida test sites. Similar growth has been reported on automotive coatings, and although the phenomenon on plastics is known among practitioners, it has not been documented in the literature. Images of microbial growth by various techniques show the morphology, often exhibited as star-shaped features 2–3 mm in diameter. Infrared techniques show the presence of protein, and profilometry shows that the features are growing on the surface and are not cracks or pits into the surface. Washing studies show that some of the growth is easily washed away but some clings strongly. •Microbial growth appears on aromatic thermoplastics after 6–12 months of weathering in Miami, Florida.•The morphology is very similar to fungal growth on coatings previously reported in the literature.•Growth can be mistaken for cracks, but analysis shows that the features are on the surface and contain protein.•Some of the growth easily washes off but some adheres tenaciously.